For more than a decade, there has been considerable effort devoted to the producing of synthetic thermoplastic sheet material having differentially colored bands or layers therein. The materials originally developed employing differentially colored bands are of the type illustrated in U.S. Pat. No. 2,985,556 granted May 23, 1961 to William P. Rowland and it can be seen that the bands of the differentially colored material extended in a direction generally parallel to the direction of extrusion. Other techniques for introducing differentially colored material in the body of the extruded sheet are shown in U.S. Pat. No. 2,632,204 to Murray and U.S. Pat. No. 2,803,041 to Hill et al.
For some applications, it is extremely desirable that the differentially colored materials not extend in a parallel pattern to the direction of the extrusion and this is particularly so in the optical frame industry wherein patterns of varying appearance are constantly desired. Various techniques have been proposed to provide interruption in an otherwise parallel pattern for the differentially colored material, among which is that illustrated in U.S. Pat. No. 3,274,646 to Krystof. Techniques for producing unusual multilayered and swirl patterns are described in U.S. Pat. No. 3,443,278 and U.S. Pat. No. 3,531,828 to Jan P. Nauta and U.S. Pat. No. 3,422,175 to William P. Rowland.
One of the most popular patterns over the past years has been a Havana pattern which effectively comprises a basketweave design wherein differentially colored material from a crosshead extruder is discharged from two series of vertically spaced ports fed intermittently by means of screws or the like. Such designs have proven quite popular but there have been very serious limitations as to the width of the sheet material which could be produced thereby due to the problems of maintaining adequate even flow of resin across the series of small ports employed.
In addition, there have been problems in maintaining reasonably distinct bands of the differentially colored material because of the tendency toward smearing as the streams of differentially colored resin and matrix resin meet and blend together.
It is an object of the present invention to provide a novel synthetic plastic sheet material having grid of bands of differentially colored resin disposed within a matrix resin and in which the bands of differentially colored material are of substantially uniform intensity and dimension throughout the width of the sheet material.
It is also an object to provide such a sheet material in which the bands of differentially colored resin are relatively distinct and substantially free from smearing.
Another object is to provide such a sheet material wherein two differentially colored resins may be utilized to provide the bands for a three color sheet material.
Still another object is to provide such a sheet material in which the differentially colored bands may cross at substantially right angles.